The present invention relates to a combined cycle power plant composed of a gas turbine plant and a steam turbine plant.
A combined cycle power plant is a power generating system which is composed of a gas turbine plant and a steam turbine plant. In this system, the gas turbine plant is operated so as to use a high temperature range of the thermal energy and the steam turbine plant is operated to use a low temperature range of the thermal energy, so that the thermal energy is efficiently recycled. Therefore, this power generating system is has attracted much interest recently.
In this combined cycle power plant, research and development of the plant are directed to raising the temperature of the high temperature area of the gas turbine, as one point for improving the efficiency.
Meanwhile, a cooling system is necessary for the high temperature area, in consideration of the heat resistance of the turbine structure, and air is conventionally used as the coolant of the cooling system.
However, in the case of using air as the coolant, even if a high temperature area is formed, this high temperature area does not produce improvements in the efficiency, because the amount of heat which is eliminated by the air which is used for cooling is increased. Therefore, there is a limit to the further improvements of the efficiency.
To overcome the above limit and to achieve further improvements of the efficiency, a cooling system using steam as the coolant instead of air has been proposed.
This type of cooling system is disclosed in Japanese Patent Application, First Publication, No. Hei 5-163960, for example. However, this cooling system has many problems which have to be overcome in its details, although it discloses the concept of using steam as the coolant.
For example, purging of the air which remains in the steam cooling system is necessary at the start of the gas turbine, and these processes are performed by the steam which is supplied by the auxiliary steam system in the above disclosed Japanese Patent Application.
However, there is no consideration of the drainage which is produced through the above series of process. Thus, the art of the steam cooling is still at the stage of trial and error, and the art for purging the drainage in the steam cooling system at the start of the gas turbine has no precedent.
Furthermore, in the conventional steam cooling system, the steam supplied by the auxiliary steam system is used for purging the air which remains in the cooling steam system, in the case of purging the air which remains in the system at the start of the gas turbine, as disclosed above. However, the oxygen concentration contained in water is increased by the air mixed with the steam at the supply of the steam for purging, and the oxygen may cause oxidation and corrosion of the pipes of the boiler.
Meantime, a drainage may be produced at the cooling portion of the gas turbine by the supply of the steam for purging. This drainage partly blocks a cooling pathway and the temperature of the metal parts of the cooling pathway shows unevenness, therefore, heat stress may be accelerated.
Moreover, if this partial blocking of the cooling pathway by the drainage is produced at a bladetip of a rotary portion or the like, moisture which is retained at the bladetip may promote the form of a super heated portion which is caused by a partial insufficiency of the cooling. Furthermore, the moisture may promote excessive centrifugal force by an unbalance of the mass, and this excessive centrifugal force may causes an accident.
The present invention is conceived in consideration of the above-described problems caused by the drainage, and has as its objective, the provision of a combined cycle power plant which can effectively purge the drainage and can certainly detects the exclusion of the drainage. In other words, the present invention has as its objective, the provision of a combined cycle power plant which can certainly detect the finishing of the warm-up process at the start of the gas turbine.
The present invention was achieved to overcome the above-stated problems.
A combined cycle power plant of the present invention is composed of a gas turbine plant and a steam turbine plant; and the combined cycle power plant has an exhaust heat recovery boiler for generating steam which drives the steam turbine using the exhaust heat from the gas turbine, and a steam cooling system for cooling high temperature cooled parts of the gas turbine by steam; and super heated steam from the steam cooling system is returned to the steam turbine. Furthermore, the combined cycle power plant has a means for detecting the flow of the steam at the gateway of the steam cooling system, and the timing of the finish of the warm-up process of the steam cooling system at the start is detected by the difference of the flow of the steam at the gateway. In case of a difference between the flow of the steam at the inlet and the flow of the steam at the outlet, of the steam cooling system, is below a permitted value, it is considered that residual air and drainage are not remained between the inlet and the outlet and the warming-up is finished, and running to the step for starting the gas turbine is enough.
Further, a combined cycle power plant of the present invention is composed of a gas turbine plant and a steam turbine plant; and the combined cycle power plant has an exhaust heat recovery boiler for generating steam which drives the steam turbine using the exhaust heat from the gas turbine, and a steam cooling system for cooling high temperature cooled parts of the gas turbine by steam; and super heated steam from the steam cooling system is returned to the steam turbine. Furthermore, the combined cycle power plant has a means for detecting the temperature of the steam at the outlet of the steam cooling system, and the timing of the finish of the warm-up process of the steam cooling system at the start is decided by the detected temperature of the steam at the outlet. For example, in case of the difference between the temperature of the steam at the outlet and the temperature of the steam at the inlet, of the steam cooling system, is below a permitted value, or the temperature of the steam at the outlet of the steam cooling system is over the saturated temperature at the supplied steam pressure, it is considered that residual air and drainage are not remained between the inlet and the outlet and warming-up is finished, and running to the step for starting the gas turbine is enough.